A nail varnish that lends a metallic appearance to a fingernail is disclosed in WO 02/03913. PVD pigments are used in this nail varnish formulation known in the prior art. Other color effects, in particular a multicolored iridescence, cannot be achieved with this nail varnish.
Pigments are marketed under the trade name SpectraFlair® by Flex Products, Inc. of Santa Rosa, Calif. (USA). The composition and manufacture of these pigments are described in the article “Advances in Interference Color,” by Barbara Parker, in the conference proceedings of the Color Cosmetic Summit, Montreal (2003). These pigments are multi-layered effect pigments created by PVD methods having an aluminum core with MgF2 layers deposited thereon. A grating with a defined spacing between grating structures is embossed on these low refracting layers. Each effect pigment produces a prismatic diffraction effect when observed under visible light. This results in a coating showing a rainbow-like effect, provided the effect pigments take on a uniform, plane-parallel orientation within a coated layer on a substrate.
In addition, rainbow effects can also be created with so-called “holographic” effect pigments. The term “holographic” effect pigments includes a plurality of effect pigments showing various structures, such as the so-called “geometric pigments” marketed by Eckart in Fuerth, Germany. In these “geometric pigments,” a plurality of polymer layers is deposited on an aluminum core by PVD methods. Said effect pigments have layer thicknesses ranging up to 10 mm and are unsuitable for cosmetic formulations, especially on account of such great layer thicknesses. The aforementioned effect pigments with grating or hologram structures, some of which are already available on the market, all have the considerable disadvantage of being relatively thick effect pigments. This disadvantage severely limits the use of said pigments in cosmetic formulations.
An additional drawback is the fact that the aforementioned effect pigments comprise relatively large particles, ie, particles with diameters greater than 25 μm.
SpectraFlair® pigments, eg, can be used in nail varnishes to produce nail varnish coatings showing a rainbow effect and a metallic appearance. Because of the great layer thickness of approximately 1 mm in SpectraFlair® pigments (Barbara Parker, “Advances in Interference Color” in the proceedings of the Color Cosmetic Summit, Montreal, 2003) and the large particle sizes of from approximately 25 μm to 35 μm, said pigments in a coating do not produce the impression of being a uniform metallic film to the observer; on the contrary, they are perceived by the observer as being individual pigments providing a glittering or sparkling effect.
Such a glittering or sparkling effect, however, is only desirable under certain conditions in cosmetic formulations such as nail varnishes. In this market, most women prefer a nail varnish showing a certain degree of elegance wherein the individual pigment particles are visually perceived as being merged into a smooth metallic film.
Moreover, the rainbow effect should not be too pronounced, as the nail varnish would then look too gaudy.
Consequently, there is a need for cosmetic formulations that provide a coating showing a fine rainbow color effect and having an elegant appearance after they have been applied.
Another disadvantage of the aforementioned effect pigments is their low covering power. The low covering power results from two effects:
On the one hand, all of the aforementioned effect pigments have relatively low contents of aluminum. In said effect pigments, however, only the aluminum core contributes to the covering power, as visible light (wavelengths of 400 to 800 nm) is reflected from only the aluminum core. The lower the proportion of aluminum core in the effect pigment, the more the covering power is reduced. Furthermore, the insufficient covering power of these pigments leads to a low coverage per unit area of the cosmetic coating composition.
On the other hand, the high layer thicknesses of said effect pigments hinder favorable stacking of the pigments in the carrier medium. Geometric pigments with layer thicknesses of 10 mm, for example, are thus completely unsuitable for use in nail varnish, as said pigments are no longer able to orient themselves sufficiently. Good orientation, in particular a substantially plane-parallel alignment to the substrate, such as a fingernail, is required in order to achieve a good visual appearance.
Furthermore, the use of said effect pigments in cosmetic compositions for producing coatings having a metallic appearance and multi-colored iridescence (rainbow effect) is not cost effective due to the very expensive and complicated processes required for their production.
In addition, rainbow effects combined with a highly metallic appearance and luster and having a good covering power can be achieved by using embossed films. For this purpose, metallized synthetic films with a grating structure are used. Such films are produced and marketed, for example, by Kurz GmbH & Co. KG of Fuerth, Germany. Such films, however, cannot be used in cosmetic formulations.